There are several types of pumps which may be used to move fluids. Basically the same type of pumps can be used for fluids which may be either liquid or gaseous. Among the many types of pumps available for such purposes are pumps which cause the fluids to move using centrifugal principals. In a pump based on centrifugal principals, a blade is provided which rotates about an axis. The blade normally includes one or more walls which are generally symmetrical about an axis so that the pump can rotate in a balanced fashion. The blade will include one or more vanes which extend radially outwardly from an inlet to an outlet. Typically the inlet is located substantially symmetrically with respect to the axis and the outlet will be an outer circumferential edge of the blade. As the blade rotates, particles of the fluid are also caused to move tangentially with respect to the axis of the blade. As the vanes cause the particles of fluid to move tangentially, centrifugal force causes the particles to move radially outwardly toward the outlet. Such devices are well-known and are referred to as centrifugal pumps.
Centrifugal pumps have found widespread usage for fluids of various kinds. Centrifugal pumps are often used as water pumps and can be used to move large volumes of water. Centrifugal pumps are also used in many applications for gases and in particular ambient air. Typically a vacuum cleaner will make use of a centrifugal blade. The negative pressure at the inlet is used as a vacuum source to remove dirt and dust from the article being vacuumed.
Centrifugal blades of this type are particularly useful in moving relatively large volumes of fluid. Centrifugal pumps are not normally the device of choice where very high ranges in pressure are required. When higher pressures are required, resort is often had to piston pumps, gear pumps or other positive displacement pumps.
Most centrifugal blades move the fluid being pumped in a direction which is substantially radial only. The blade is housed within a shroud to direct fluid flow as desired. The pump comprising the blade and its shroud is then driven by a motor. Typically the motor shaft is attached to one of the walls of the blade. As long as the wall of the blade to which the drive shaft is attached is substantially planar, the length of the drive shaft between the locations of fixation to that wall and the motor can be conveniently short.
Theoretical considerations have also given rise to a type of pump some times referred to as a combined flow or mixed flow pump. In a mixed flow device, the blade is provided with a taper so that the fluid particles moved by the vanes move in a direction which is primarily tangential and radial, but which also includes a component which is axial, that is the fluid particles move in a direction having a component which is parallel to the axis of rotation of the blade. Such blades are not generally well accepted, as the blade must then have an increased axial length as compared with a blade of similar diameter which imparts only tangentialradial flow to the fluid being moved. This in turn means that the motor must be positioned farther from the surface of the blade to which the drive shaft is attached. Lengthening the drive shaft creates a greater mass of rotating material as well as increasing stability problems arising from the se of the greater overall length of the pump and motor unit. This in turn ay call for additional bearing structures.
Centrifugal fans of the pure tangential radial type are thus the referred choice. Pumps of this type have been well accepted and are widely used, particularly in the vacuuming industry for household vacuums. In most household vacuums, a motor is fitted to the blade for driving the blade. The motor typically operates off household current and a cord is provided. One of the draw backs of this type of arrangement is that the vacuum cleaner can only be used at a distance from the supply of household current determined by the length of the cord. This means, as the vacuum is used to clean a larger area, the cleaner must shut off the vacuum from time to time, unplug the cord and move the cord to another outlet within the next area to be cleaned so that all portions of the desired area can be reached within the limitations provided by the cord length. It is inconvenient to provide excessively long cords as the cord itself then becomes more trouble to handle in order that it be kept coiled and uncoiled as necessary, depending upon the length from the outlet.
Various attempts have been made to create household vacuums which operate on battery or other portable power. Such devices are particularly useful in small hand held size for doing light cleaning jobs. In such units, power is often provided by on-board batteries which may be of a rechargeable nature. The vacuum operates for a relatively short period of time, perhaps five to ten minutes, and a relatively low powered vacuum pump is included. The unit may then be moved from place to place providing low power vacuum over a relatively short period.